The present invention relates generally to matrix and equalizer circuits and more particularly to an equalizing circuit for a multichannel record reproducing apparatus.
The matrix circuit applies the sum and difference signals into respectively individual channels in a multichannel record reproducing apparatus. An added circuit imparts a specific frequency characteristic thereby doubling as an equalizer circuit.
THE DISCRETE 4-CHANNEL RECORD DISC SYSTEM SHOWN IN U.S. Pat. No. 3,686,471 provides a direct wave of the sum signal of a pair of two channels and an angle-modulated wave obtained by angle modulating a 30 KHz carrier wave responsive to the difference signal of a pair of two channels. The direct and modulated waves are superimposed and recorded on the side wall of the disc sound groove.
In order to attain interchangeability in reproduction between this 4-channel record and the conventional 2-channel stereo record, the recording process is carried out in the 4-channel recording system by causing the signals to have an equalizer characteristic comforming to the standard specification of the Record Industry Association of America (RIAA). Therefore, the 4-channel record reproducing system must equalize according to the RIAA equalizer characteristic. To obtain this specific characteristic, as described hereinafter, the multiplexed signal reproduced from the pickup cartridge is passed through an RIAA turn-over equalizer circuit. A direct-wave sum signal is obtained by further separating it therefrom as it is passed through a specific RIAA roll-off equalizer circuit.
The angle-modulated difference signal obtained by separation from the multiplexed signal which has thus passed through the RIAA turn-over equalizer circuit is then demodulated. The difference signal thus demodulated and the sum signal, which has passed through the RIAA roll-off equalizer circuit, are introduced into a matrix circuit and thereby matrixed to obtain four separate channel signals.
In the previous 4-channel record reproducing systems, this matrix circuit has an operational circuit of zero gain which is totally separate from the equalizer circuit. Therefore, since an equalizer circuit and an ordinary matrix circuit are required, the entire circuit becomes unecessarily large.
With the aim of miniaturizing the circuit, a block form or IC form may be adopted for use as the matrix circuit so that it will have gain. The noise from the equalizer circuit in the preceding stage will no longer be negligible. If the gain of the matrix circuit in IC form is made small enough to make noise negligible from the equalizer circuit, it will be necessary to provide an amplifier in the stage following the matrix circuit, in which case, the advantage of forming the matrix circuit as an IC will be lost.